Wide bandwidth radio frequency amplifiers are used to amplify a plurality of radio frequency channels over a bandwidth that is typically around about 1000 MHz wide. Due to their ability to amplify signals over such a large bandwidth, wide bandwidth radio frequency amplifiers are key components in cable television (CATV) infrastructure. An important performance criterion for wide bandwidth radio frequency amplifiers for CATV infrastructure includes linearity as measured relative to composite intermodulation noise (CIN) and composite triple beat (CTB). Other important criteria are linearity and gain performance over temperature.
A particularly useful wide bandwidth radio frequency amplifier configuration for CATV infrastructure is known as a push-pull cascode amplifier. FIG. 1 is a simplified schematic of a related art wide bandwidth radio frequency amplifier 10 having a push-pull cascode configuration suitable for radio frequency signal amplification. The related art wide bandwidth radio frequency amplifier 10 includes a first signal path 12 having a first input 14 and a first output 16. A first field effect transistor FET1 and a second field effect transistor FET2 in the first signal path 12 are coupled in a cascode configuration. The first field effect transistor FET1 is manufactured using gallium arsenide (GaAs) technology on a first single amplifier die 18, while the second field effect transistor FET2 is manufactured using gallium nitride (GaN) technology on a second single amplifier die 20. A first gate G1 of the first field effect transistor FET1 is coupled to the first input 14 and a source S1 is coupled to ground GND through a first resistor R1. A drain D1 of the first field effect transistor FET1 is coupled to a source S2 of the second field effect transistor FET2. A drain D2 of the second field effect transistor FET2 is coupled to the first output 16.
The related art wide bandwidth radio frequency amplifier 10 also includes a second signal path 22 having a second input 24 and a second output 26. A third field effect transistor FET3 and a fourth field effect transistor FET4 in the second signal path 22 are coupled in a cascode configuration. The third field effect transistor FET3 is manufactured using gallium arsenide (GaAs) technology on a third single amplifier die 28, while the fourth field effect transistor FET4 is manufactured using gallium nitride (GaN) technology on a fourth single amplifier die 30. A gate G3 of the third field effect transistor FET3 is coupled to the second input 24, a source S3 is coupled to ground GND through a second resistor R2. A drain D3 of the third field effect transistor FET3 is coupled to a source S4 of the fourth field effect transistor FET4. A drain D4 of the fourth field effect transistor FET4 is coupled to the second output 26. A third resistor R3, coupled between the first source S1 and the third source S3, along with a fourth resistor R4, coupled between the second gate G2 and the fourth gate G4, provide symmetry of operation that generates a virtual ground, which in FIG. 1 is represented by a dashed line.
The related art wide bandwidth radio frequency amplifier 10 further includes an unbalanced-to-balanced transformer TF1 having a radio frequency input RFIN at a pad P1 that is coupled to ground GND through a first winding N1. A first phase output 32 is coupled to the first input 14 of the first signal path 12, and a second phase output 34 coupled to the second input 24 of the second signal path 22. A balanced-to-unbalanced transformer TF2 has a first input winding N3 with a first phase input 36 coupled to the first output 16 of the first signal path 12, and a second input winding N4 with a second phase input 38 is coupled to the second output 26 of the second signal path 22. The first input winding N3 and the second input winding N4 are coupled in series at a node 40. A supply voltage VDD is provided through a pad P2 that couples to the node 40. A radio frequency output RFOUT at a pad P3 is coupled to ground GND through an output winding N5.
While the related art wide bandwidth radio frequency amplifier 10 performs relatively well, it is desirable to realize a wide bandwidth radio frequency amplifier with improved linear performance with regard to CIN and CTB as well as realize improved linear performance over temperature with higher gain. Moreover, it is desirable to reduce the number of passive components and active component dies needed for proper operation of wide bandwidth radio frequency amplifiers.